Fire and smoke alarm devices are designed to respond to a selected temperature or a selected condition to cause actuation of a signal which provides an audible warning. Some fire alarms are mechanically actuated and include mechanical alarm means. An example of such an alarm device is that shown in U.S. Pat. No. 3,570,446 issued Mar. 16, 1971 owned by a common assignee.
In the fire detection alarm means of said patent, a trigger means was cooperably connected with a thermal responsive device which included a bimetallic disc adapted to snap from a convex shape to a concave shape and during such transition, to forceably contact an axially movable spacer element. The inner end of the spacer element provided a seat for one end of an axially displaceable pin which carried a shoulder upon which was seated a lever trigger member which released the mechanical alarm. Precise positioning of the several parts of the triggering device in relation to the bimetallic disc and the actuating alarm lever was required to assure reliable actuation of the triggering device for actuation of the alarm. Manufacturing tolerances and friction between the several parts made such setting a delicate, relatively time-consuming operation. Because the forces involved as initiated by the bimetallic disc were not of large magnitude, adjustment of the triggering device at the factory was required to be precise and the presence of dust or foreign particles, and thermal expansion or constraction or deformation of components caused by stressing when installed for a period of time might cause the triggering device to be inoperable.
There is, therefore, a need for a triggering device for such an alarm which did not require precise assembly, adjustment, and manufacturing tolerances.